Depends on their proficiency points and how you build them. Lezalit could be a heavy hitter with a 2-handed sword and plate mail, while Alayen could be a sword and shield guy.
Most NPCs when you hire them have an equal number of proficiency points in each category. It's mainly how you build them as you level up.
In field battles, the two-handed weapon compares very well against "sword and board", and can sometimes be the preferable on horseback. Once you start sieging castles, the shield starts to make a difference, providing some defense against ranged attacks while they climb the ladders. There's nothing to stop you from arming some of your companions each way, rather than use a "one size fits all" approach.